Numerous methods exist for cutting parts out from a sheet or plate or material using templates of predetermined shapes and sizes. A placer puts templates having the shapes and sizes required for the parts onto the sheet or plate of material and generally seeks to avoid having templates which overlap; thereafter the material is cut along the outlines defined by said templates.
However, in some particular applications, it may be acceptable, or indeed desirable, to allow templates to overlap during placing so long as the overlaps do not significantly spoil the quality of the finished product, for example this may save raw material.
Also, templates overlaps may be the result of inaccurate placing or of an error in the system for inputting the positions of the templates when such a system is used in the cutting out process, prior to cutting out per se.
In prior art methods, two cases may arise in the event of an overlap.
If cutting out is performed on a first-takes-all basis, then the first overlapping part to be cut out is good and the second has a defect. Unfortunately it is difficult to establish simple criteria for reliably selecting the order in which parts should be cut out.
If cutting out is performed automatically, for example by means of a laser or a water jet, both parts are fully cut out, and as a result their intersection is lost from both of them. Each part then has a defect corresponding to the full size of the overlap from the other part. This is shown in accompanying FIGS. 5a and 5b: in FIG. 5a two templates 1 and 2 are shown in part, and they have outlines which overlap to give points of intersection 4 and 5 and an overlap zone 3 which is shown shaded; FIG. 5b shows portions of the parts 1' and 2' of sheet or plate material as they would be cut out using prior art automatic methods. Each of parts 1' and 2' corresponding respectively to the templates 1 and 2 has a full defect corresponding to the entire overlap mark of the other part, and a part 3' corresponding to the overlap zone 3 is lost from both parts 1' and 2'.
One of the aims of the present invention is to provide an automatic cutting out method which makes it possible to select in advance the consequences of at least two templates overlapping, regardless of whether the overlap is voluntary or otherwise.